1. Field of Invention
The present invention relates, in general, to the inspection of pipe coatings and, more specifically, to a tether-free piggable inspection device capable of reading and storing data relating to holiday detection and pipeline coating thickness in very long pipelines.
2. Description of Related Art
Internal non-conductive coating in pipelines provides protection, prevents corrosion, and improves the rate of liquid and gas transfer. In order for the pipe to be adequately protected, the layers of coating must be uniform, continuous and in compliance with the range of thickness values specified by the client. To verify these conditions, it is necessary to perform tests either between coating layers or after the final coat is applied. If a defect is found, a new coat will be applied and a new test must be run to certify the repair success.
Coating thickness measurement and holiday detection (holidays are also known as pinholes, voids, discontinuities, etc.) are two very common procedures that can provide an accurate diagnosis of the coating integrity. Among several methods, thickness measurement can be performed by using magnetic induction, Eddy currents or ultrasound waves; depending on the coating and pipe structures. Holiday detection is most commonly performed by positioning the coating between the positive and negative terminals of a high voltage power supply creating a high resistance path unless a coating discontinuity is present, in which case the circuit will close triggering an alarm.
Conventional testing devices utilize one of the two above mentioned procedures; they either measure coating discontinuities (i.e., the presence of a holiday) or coating thickness. Moreover, most of these tools are used for external measurement, and, in case the measurement is internal to the pipe, the tool's reach is limited to few feet. There is a need in the art for an inspection tool which monitors the internal coating integrity throughout the entire length of the pipeline which, in the case of a coiled tubing or flow line pipes, can be as long as several thousand feet.
It is an object of the present invention to provide a state of the art pipeline inspection tool that will perform coating thickness measurement and holiday detection for internal pipe inspections, tether free and battery operated.